Printing of corrugated board



y 1959 R. w. JONES 2,893,320

PRINTING OF CORRUGATED BOARD Filed March 29. 1956 'Illlllllllllle 'INVENTOR. Rexford W. Jones z www i ATTORNEYS.

United States Patent PRINTING or CORRUGATED BOARD Rexford'W. Jones, Columbus, Ohio, assignor, by mesne assignments, to Fort Wayne Corrugated Paper Company, Fort Wayne, Ind.

. d 1 Application March 29, 1956, Serial No. 574,647 8 Claims. or. 101-426) :is comprised of one corrugated, or fluted, sheet which is glued between,two flat facing liners. The facing liners .are in contact with the corrugated sheet along the apices of the'corrugated sheet, Multiwall corrugated board, as

.theinar'ne implies, is comprised of, additional alternate corrugated sheets and facing liners in addition to those comprising the double-faced corrugated board. The most commontype is double-wall corrugated board which is comprised of, in the following sequence, a facing liner, a corrugated sheet, a flatliner, another corrugated sheet, jandjanother facing liner. Although not apparent to casual observation, the surface of the corrugated board containsj flutes or grooves in the facing liner corresponding Itiith corrugations of the corrugated sheet immediately beneath'the facing liner.

At the present time, the printing on corrugated board is done primarily by. means of direct printing from a relief form, such as a rubber die. To the best of applicants knowledge, it has been the commonly accepted understanding and experience of those skilled in the art that 'the grooved surface of the facing liner of corrugated board and the resiliency of the board prohibited satisfactory printing of the corrugated board by any other printing process except by direct printing from a rubber die. This methodof printing, although completely reproducing the inked image invrelief on the rubber die, is seriously restricted as to the quality of reproduction and the nature of the images which may be desired to be printed on the corrugated board. Theimages reproduced by "direct printing on corrugated board have very little, if -any,'tonal quality and,,as a result, are rather crude in appearance. Attempts at printing halftone subjects from rubber dies have resulted in exaggeration of the flutes in the corrugated board and streaked appearance of the prints. This is due principally to differences in the printing pressure of the small halftone'dots, depending upon whether the dots strike the facing liner along the portions supported by the apices of the corrugations underneath the liner or strike in the unsupported recessed areas be- :tween the corrugations. Also, the reliefthatcan be obtained in rubber halftone dies is limited, inking conditions being very critical to prevent flooding of the die and distortion of tone values. General printing pressure is also criticalwith rubber halftonedies, the variations in caliper of the board making the control of conditions .very. difiicult. Due to the characteristics of the rubber die and the manner in which the images aremade on the die it is not possible to reproduce images of any great r ce complexity. Because of the crude appearance and the simple nature of design, the printing on corrugated board lacks effectiveness for artistically displaying, for example, the contents of the corrugated board carton. The printing on the corrugated board, therefore, serves primarily merely to identify the contents of the carton and has limited advertising value.

Applicant has discovered that by the use of an offset blanket having an effective surface hardness of from 20-40 durometer, it is possible to print upon the facing liner of corrugated board by the dry relief offset process. In accordance with this invention, it is possible to obtain substantial and remarkable gain in general image quality. .The prints obtainable, following the practice of this invention, are sharper and reproduce in much finer detail than is possible with rubber dies. Extremely small type, fine lines, and even -line halftone engravings can be produced with good fidelity of reproduction, thereby afiording considerable flexibility in the kinds of images that can be produced. Thus, it is even possible to print photographed subjects on the corrugated board. Among other advantages of the dry offset process of printing corrugated board in accordance with this invention is the elimination of distracting exaggerations of the flutes in the printed area. The image to be printed is transferable with precision from the dry relief offset plate to the smooth uniform surface of the offset blanket. The high quality image on the blanket is then transferable to the facing liner on the corrugated board without distortion of dots and, consequently, tone values, and, furthermore, without excessive printing pressure that would deleteriously affect the strength of the corrugated board. The artistic and realistic effects obtainable in accordance with applicants invention opens a completely new approach to the printed design of corrugated board.

Fig. 1 is a schematic diagram of a rotary offset printing machine.

Figs. 2 and 3 show conventional structures of ofiset blankets for dry relief offset printing. Fig. 2 is an enlarged sectional view of a rubber blanket having a single fabric layer 8 as a backing for the rubber layer. The surface of the rubber layer 9 bears the inked image to be printed. Fig. 3 is an enlarged fragmentary view of an offset blanket built up of interlayers of rubber and fabric. Structurally, this offset blanket consists of a base rubber layer 10, followed by a fabric liner 11, a rubber layer 12, another fabric liner 13, and a rubber layer 14. The surface of the rubber layer 14 bears the inked image to be printed.

Referring to Fig. 1 for a description of the process of 3 printing corrugated board on a rotary ofiset machine, the

corrugated board 6 is passed into pressure contact with the surface 5 of the rubber offset blanket 4 which, in the case of printing corrugated board, must have a hardness, when positioned on the blanket cylinder 3, of not less than about 20 and not more than about 40 durometer. The board 6 is maintained in pressure contact with the offset blanket 4 by the impression cylinder 7 which is in contact with the underside of the board as shown in the drawing. The printing pressure applied to the board is determined by the distance between the surface of the impression cylinder and the surface 5 of the offset blanket. The printing pressure can be varied by decreasing or increasing the distance between the impression cylinder surface and the surface of the offset blanket. As illustrated below, the printing pressure must not be too great or otherwise the board will suffer printing crush and cause a decrease in the strength of the board. As the board 6 is impressed against the surface 5, the inked image thereon is transferred to the facing liner of the {board The inked image transferred from the surface 5 of the offset blanket 4 has previously been received from the inked image on the dry relief plate 2 positioned on the plate cylinder 1.

In conventional printing by the dry relief offset process, it has been the general understanding thatthe rubher oifset 'blanket should have a surface hardnessof from 70-75 durometer in order to accept *a clean image from the relief plate Without slipping or squeeging." The result .of slippingor squeeging is a double image -or smearedimage. "Conventional offset blankets of 70- 75 durometer hardness, it was found, "printed only on the ridges present in the facing liner of the corrugated board, these ridges corresponding 'to the apices of the corrugations beneath the facing liner. incomplete transfer of the imagexresulted, veventhough=the'printing pressure was increased to the point where the corrugated board was damaged. However, .applicant has discovered that by .using rubber offset blankets having an effective surface hardness, when positioned on the blanket cylinder, of from about .20 to '40 durometer and preferably '25 to 3'5 durometer, .excellent printing of corrugated board by the dry relief process is possible. Within this range of hardness, the rubber offset blanket 'is capable of accepting the pressure from the inked relief plate for transfer of the inked image to the blanket without slipplug or sgueeging. At the same'time, the offset 'blanket, having a surface hardness withinthis range, is suffic'iently resilient to conform to the fluted or grooved areas in the surfaceliner of the corrugated board to transfer the inked image with precision to the surface liner without distracting variations .in image density over the flutes. Otfset'blankets having aneffective surface hardness .of greater than 40 durometer reproduce images of varying density correspondingto the fluted areas of the surface liner. With offset "blankets of less than durometerhardness, slipping and'otfset occur in the transfer of the image from the relief plate to the blanket and blurred and .indistinct images are printed on the corrugated board. Thus, applicant has satisfied at least two diametrically .opposed requirements in dry relief offset printing by the discovery that offset blankets having effective surfacehardnesses of from 2040 durometer permit corrugated board to be printed by the dry relief offset process.

As previously indicated, it is now possible to print type, images, .and designs of greater complexity, clarity, and advertising appeal than heretofore possible with .direct relief printing of corrugated board, such as by means of rubber relief plates or dies. The following are examplesof the variety of subjects which were printed with good quality .by .dry relief offset printing using a rubber blanket comprisedof a single fabric backing and a layer of rubber engravers gum having an effective surface hardness of 35 durometer. The term effective surface hardness is used herein and in the claims to mean the surface hardness .of theolfset blanket when properly stretched and snugly fitted around the blanket cylinder. High-quality prints were obtained from dry relief ofiset plates containing a 65-line photoengraving, a solid area, and various sizes of type and lines. Prints also were made from 85-line and l20-line photoengravings, line drawings, and combination plates. The halftones were faithfully reproduced, although some of the 120-line prints did not show up to best advantage on the tan facing liner of the corrugated board. For the most part, .the coarse-screen prints gave the most pleasing appearance on the tan liner. The prints consisting of and AD-line photoengravings indicate that these are most practical for printing on corrugated board, although the :tonal range and amountofdetail in the subjectultimately determine the best screen size. These prints were all made on a modified letter press proof press Whereinthe impression-cylinderwas modified to be'used as a blanket cylinder.

Further prints were made -on.a rotary relief printing machine with a dry offset plate containing a variety of images and typesof printing. The plate was 0.032-inchthick zinc etched to a depth of about 0.012 inch in nonprinting areas. The maximum depth of etch in the halftone areas was about 0.006 inch. The plate contained a halftone tone scale, a solid area, a line drawing, and various sizes of type and lines. The type included 6 point, 12 point, 60 point, 72 point, and a section of 24- point reverse type. Printing runs were made with this relief plate, using offset blankets of different surface hardnesses. In the first run, a rubber blanket made of engravers gum with fabric interlayers and a rubber back in the manner shown in Fig. 3 was used. This blanket had a surface hardness slightly greater than 35 durometer in a free position,.and an effective surface hardness of about 40 durometer when placed in position on the blanket cylinder. In the prints obtained from run using the 40-durometer offset blanket, the flutes were somewhat apparent and the solid coverage was not so intense and uniform as desired. The next run was made with -an offset blanket having a durometer hardness of 35 when mounted on the impression cylinder. The prints obtained with the S'S-durometer blanket gave improved solid coverage 'and'the appearance of the flutes'was not distracting. The 35-durometer blanket was then removed and in 'its place 'was inserted a similar :blanket of engravers rubber having an effective surface hardness of about '30 durometer. Improved results were immediately apparent with" this blanket. The appearance of 'the flutes was essentially eliminated and solid coverage was more uniform. Contrary to expectations, no difficulties were encountered in transferring the image from the relief plate'to the surface of this 30adurometer rubber blanket. The use of this blanket resulted in prints of exceptionally high quality.

A further run was made using a similarly constructed rubber blanket made of standard engravers gumhaving an effective surface hardness of 2S durometer. Again, there was a significant improvement in results over the SO-durometer blanket. Coverage between the flutes was improved and uniform coverage of solids was obtained.

'The offset blanket may be a composite of rubber layers of different hardnesses, the surface layer of which, alone, "has a hardness greater than the maximum of 40 durometer. Thus, satisfactory offset blankets were made Whereinthe top rubber layer consisted of a base layer of engravers rubber of about 20 to 30 durometer and a thin layer of SO-durometer rubber molded on the surface. Such blankets having .a layer of about 0.012 to 0025 inch thickness of 50-durometer rubber on a base layer of about 20 30 durometer had an effective surface hardness of from about 30-35 durometer. In this manner, it is possible to obtain the benefit of the harder rubbers greater resistance to ink penetration while still maintaining the effective surface hardness within the range .of about .2040 durometer.

Contrary to expectations, excessive printing pressure is not necessary to obtain proper and complete transfer of the inkedimage from the offset blanket to the facing liner on the corrugated board. The corrugated board can be printed without being subjected to any printing crush or only such slight amount that it does not reduce the strength of the board. Thus, for a B-flute board with a caliper of about 0.130 inch, a separation of about 0.110 inch between the offset blanket and impression cylinder produces a goodprint withno measurable-printing crush. In offset printing, unlike printing :from rubber dies, the printing .pressureis supported over :the entire Widthofzthe board. 'The.0;020-inch :compressionof the board, which is partiallyabsorbed by the .offset blanket, does not result in permanent crush. Decreasing the spacing between the offset blanket and impression cylinder, ithrough whichthe corrugated board passes, :to about:0.080-inch clearance, results in about=0;009ito 0.010-inch.:crush, but has no .sub-

.aspects.

s eam stantial,. effect on print quality. A slight improvement in solid coverage may be obtained with increased pressure buttheimprovement is so'slight as to be practically negligible. Most of the prints previously described on the rotary offset machine. were made with a spacing of about 0.100 to 0.105 inch between the offset blanket and the impression cylinder. The main reason for using more than. the printing pressure for no permanent crush was to insure'printing in slightly damaged or depressed areas of the'board. For the purpose of illustrating the effect of printing pressure on crush and strength of the corrugated board, several runs were made on a rotary offset press under various printing pressures using an offset blanket having an effective surface hardness of 30 durometer. These runs are tabulated below:

Retained Com- Dlstance presslve Strength, Between Approximate percent Series Blanket and r g Impression Crush, inch Cylinder, inch Top to End to Bottom End Contr 100 100 A 0. 11 0. 000 100 100 0. 0. 003 100 100 0. 09 0.005 to 0.006 85 75 to 80 0. 08 0.009 to 0.010 70 60 Compression results calculated from puncture and flat crush tests.

A printing crush of about 0.003 to 0.004 inch can be tolerated with decreasing the strength of the corrugated board. This allows suflicient leeway so that the printing pressure need not be continually and critically adjusted during high production printing runs. Generally, it is preferred that the printing crush should not exceed about 0.004 inch, the maximum amount of crush which is presently permitted in the printing of corrugated board by means of rubber relief dies. As shown, proper and uniform printing is obtained by the dry relief offset process without exceeding this amount of crush.

Rubber of the same kind as used in conventional blankets of 70 to 75-durometer hardness or rubber engravers gum may be used in the rubber blankets of 20 to 40-durometer hardness, the difference in hardness being obtainable by conventional formulation techniques known in the art. Representative examples of rubber used in offset blankets are the synthetic rubbers made by the copolymerization of butadiene and acrylonitrile. Most generally, the filler determines the hardness of the rubber, and, in the case of the rubber in the conventional offset blanket, the filler, such as carbon black, may be present in amounts as high as 75 parts by weight of the rubber.- Rubber of a hardness below about 45 durometer is obtained by lesser amounts of filler and larger amounts of plasticizing agents, such as tn'cresyl phosphate. The butadiene acrylonitrile rubbers are particularly suitable for offset blankets because of their good oil resistance.

Thus, by means of an offset blanket in accordance with this invention, uniform and proper coverage of the printed image on the fluted or grooved surface of corrugated board can be obtained by dry relief offset printing. Corrugated board of various kinds can be printed, including in addition to singleand multi-wall board, single-faced corrugated board. Single-faced corrugated board is similar to single-wall board except that the corrugated, or fluted, sheet is adhesively united to a flat sheet or facing liner along the apices of the corrugations on only one side of the corrugated sheet. Unlike the single-wall board, the single-faced corrugated board can be rolled about an axis parallel to the direction of its flutes or corrugations. From the particular embodiments of this invention as described herein, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the invention in its broader Accordingly, the appended claims are intended to cover all such changes and modifications as fall the true spirit and scope. of the invention. What is claimed is:

1. In the process of dry relief offset printing of cor-' rugated board, the steps comprising: contacting an inked dry relief plate against the surface of a rubber offset blanket having an effective surface hardness of about 20-40 durometer to'transfer an ink image on said offset blanket and contacting corrugated board against said offset blanket to transfer the ink image thereon to the facing liner of the corrugated board without deleteriously affecting the strength of the corrugated board.

2. In the process of dry relief offset printing of corrugated board, the steps comprising: contacting an inked dry relief plate against the surface of a rubber offset blanket having an effective surface hardness of about 25-35 durometer to transfer an ink image on said offset blanket and contacting corrugated board against said offset blanket to transfer the ink image thereon to the facing liner of the corrugated board without deleteriously affecting the strength of the corrugated board.

3. In the process of dry relief offset printing of corrugated board, the steps comprising: contacting an inked dry relief plate against the surface of a rubber offset blanket having an effective surface hardness of about 2040 durometer to transfer an ink image on said offset blanket and impressing corrugated board against the offset blanket to transfer said ink image to the facing liner of the corrugated board without imparting to said cor rugated board a permanent crush greater than about 0.004 inch.

4. In the process of dry relief offset printing of corrugated board, the steps comprising: contacting an inked dry relief plate against the surface of a rubber offset blanket having an effective surface hardness of about 25-35 durometer to transfer an ink image on said offset blanket and impressing corrugated board against said offset blanket to transfer said ink image thereon to the facing liner on the corrugated board without imparting to said corrugated board a permanent crush greater than about 0.004 inch.

5. In the process of dry relief offset printing of corrugated board, the steps comprising: contacting an inked dry relief plate against the surface of an offset blanket having an effective surface hardness of about 20-40 durometer to transfer an ink image on said offset blanket and contacting corrugated board against said offset blanket to transfer the ink image thereon to the facing liner of the corrugated board without deleteriously affecting the strength of the corrugated board.

6. In the process of dry relief offset printing of corrugated board, the steps comprising: contacting an inked dry relief plate against the surface of an offset blanket having an effective surface hardness of about 25-85 durometer to transfer an ink image on said offset blanket and contacting corrugated board against said offset blanket to transfer the ink image thereon to the facing liner of the corrugated board without deleteriously affecting the strength of the corrugated board.

7. In the process of dry relief offset printing of corrugated board, the steps comprising: contacting an inked dry relief plate against the surface of an offset blanket having an effective surface hardness of about 20-40 durometer to transfer an ink image on said offset blanket and impressing corrugated board against the offset blanket to transfer said ink image to the facing liner of the corrugated board without imparting to said corrugated board a permanent crush greater than about 0.004 inch.

8. In the process of dry relief offset printing of corrugated board, the steps comprising: contacting an inked dry relief plate against the surface of an offset blanket having an effective surface hardness of about 25-35 durometer to transfer an ink image on said offset blanket 7 8 gn d impressing corrugated board against said offset 2,278,980 4 Frolich fi Apr. 7, 1942 blanket i0 transfer said ink image. thereen to the -fagzipg 2,333,800 Lewis; et a1. u Nov. 9,194} liner of the corrugated board without imparting to said 2', 48Q, 79 :1f lile'sjet al ,'N c)v. 29, 1949 corrugated board a permanent crush greater than about 2530 282- Bmdie et a1. Nov. 14, 1950 0.004 -1nch. 5 REFERENCES,

.Ref ren e'srcited in the 'file 'of this patent C Elli: Piilt ifli Inks,l pub. 1940 by Reinhold Pub.

I 911 New or On y'page 302 made '0f' record, UNITE? STATES PATENTS 0 Haeklei uan: Commercial Engraving and Printing, pub. 1640,44? Corbm m 1921 byiCommerci'al Engraving Pub. 00., Indianapolis. 2,014,043 Harblson Sept. 10, 1935 ofi 506 made bf-l-ecordv 2,036,835 Sites Apr. 7, 1936 2,054,620 Freedlander Sept. 15, 1936 

